linux-kernel - RE: [PATCH 09/12] unicore32 machine related files: hardware registers

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Date:	Sun, 27 Feb 2011 11:35:05 +0800
From:	"Guan Xuetao" <gxt@...c.pku.edu.cn>
To:	"'Arnd Bergmann'" <arnd@...db.de>
Cc:	<linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
	"'Greg KH'" <greg@...ah.com>
Subject: RE: [PATCH 09/12] unicore32 machine related files: hardware registers



> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@...db.de]
> Sent: Saturday, February 26, 2011 9:16 PM
> To: Guan Xuetao
> Cc: linux-kernel@...r.kernel.org; linux-arch@...r.kernel.org; 'Greg KH'
> Subject: Re: [PATCH 09/12] unicore32 machine related files: hardware registers
> 
> On Saturday 26 February 2011, Guan Xuetao wrote:
> > > >  #ifndef __ASSEMBLY__
> > > >
> > > > -# define __REG(x)      (*((volatile unsigned long *)io_p2v(x)))
> > > > -# define __PREG(x)     (io_v2p((unsigned long)&(x)))
> > > > +# define __REG(x)      (void __iomem *)io_p2v(x)
> > >
> > > The patch looks correct, but if you make the the definition for
> > > PKUNITY_MMIO_BASE contain the cast to (void __iomem *), you no
> > > longer need another cast.
> >
> > Because the io_p2v(x) calculate x and PKUNITY_IOSPACE_BASE,
> > all registers should be added with (void __iomem *).
> > So I prefer to remain the previous patch.
> 
> The problem with the definition of io_p2v is that it gives you
> an type that is impossible to use correctly, except in assembly
> code. Linux assumes that MMIO registers in virtual space
> are __iomem pointers, and we like that to be consistent.
> 
> If you have a function that returns a virtual address, it should
> really have the same type as any other function that uses a virtual
> address.
Ok, I see.
Please see following patch, __REG removed and __iomem added to io_p2v:

diff --git a/arch/unicore32/include/mach/hardware.h b/arch/unicore32/include/mach/hardware.h
index b71405a..b197b0b 100644
--- a/arch/unicore32/include/mach/hardware.h
+++ b/arch/unicore32/include/mach/hardware.h
@@ -17,13 +17,10 @@
 
 #include "PKUnity.h"
 
-#define io_p2v(x)	((x) - PKUNITY_MMIO_BASE)
-#define io_v2p(x)	((x) + PKUNITY_MMIO_BASE)
-
 #ifndef __ASSEMBLY__
-
-# define __REG(x)	(void __iomem *)io_p2v(x)
-
+#define io_p2v(x)	(void __iomem *)((x) - PKUNITY_MMIO_BASE)
+#else
+#define io_p2v(x)	((x) - PKUNITY_MMIO_BASE)
 #endif
 
 #define PCIBIOS_MIN_IO			0x4000 /* should lower than 64KB */
> 
> 	Arnd
Thanks & Regards.
Guan Xuetao

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